Fast neutron detection with coincidence counting of recoil tracks in CR-39

Abstract

Unpredictable background is often the major drawback in the assessment of low fluences of fast neutrons with solid state nuclear track detectors. The problem can be effectively solved by counting coincidence tracks in two detector foils that are in close contact during the irradiation. The detection of fast neutrons performed with a pair of CR-39 detector foils, subsequent chemical etching and evaluation of the etched tracks by an automatic track counting system was studied. After counting, only tracks produced by the same recoil nuclei in the surface layers of both detector foils were taken into account. In this way, the background due to objects that cannot be separated from tracks by an automatic counting system was drastically reduced. Emphasis was given to determining the properties of such a coincidence fast neutron detector based on utilisation of CR-39. The response of the coincidence detector was found to be 3×10 −5 tracks/neutron and is comparable with a detector based on counting tracks in a single foil of CR-39. The lower neutron detection limit was found to be 2×10 4 cm −2 with a counting area of 10 cm 2, and is two orders of magnitude lower than that obtained with a detector based on counting tracks in a single foil of CR-39.